I went from Rubena Flash 28(a junk), to 28 CST (another junk) to Continental GP3000 622x20 (that is quite good and in 5years i had only one flat and i ride only on asphalt (but it's seriously degraded with holes-bumps-rocks-dust-cement-etc in/on it.. administrative part of my city are not doing their job properly.. )
I saw an improvement right away, and trimmed off 700grams in total, from 500g/tire, to 180g/tire, and at 30-50$ are very nice tires fold-able, lite, with kevlar/vectran. That improvement is about how i feel and how fast i get tired, I'm not a professional rider, and I do not keep track of my performance, and that was some 5years ago.